1. Field of the Disclosure
This disclosure relates to a projection system, and, more particularly, to a low Z-height projection system for projecting structured light for 3D imaging.
2. Background
Recently, small footprint projectors using liquid-crystal-on-silicon (LCOS) or digital-light-processor (DLP) display panels known as pico projectors have been available. Pico projectors are small portable projectors. Due to its compact size, a pico projector may be included in a mobile phone, so that the mobile phone can project the display onto any surface such as wall.
A pico projector may include a small LCOS display panel, which may be transmissive type or reflective type. Typically, a pico projector includes one or more light sources, a beamsplitter, an LCOS display panel, and a projection lens. Furthermore, the pico projector may be used for projecting structured light for 3D imaging. Typically, the structured light for 3D imaging includes a vertical grating pattern. The vertical grating pattern is projected onto a surface having a profile. The profile at a position, e.g., a protrusion or a recess relative to a flat surface, can be calculated from the deformation of the projected grating at that position. The deformation typically relates to the horizontal shift of the projected vertical grating from its image if the surface is flat without a profile.
A 3D imaging system includes a projector for projecting the structured light and a digital camera for detecting the deformation of the projected structured light. The 3D imaging system may further include a computer or a digital processor. It often requires that the projector be small, in order to reduce the overall dimensions of the 3D imaging system. In addition to providing the profile of a static 3D object, the 3D imaging system may also be used for gesture recognition for controlling a computer, gaming, as well as many other uses. A small projector for projecting structured light for gesture recognition is in especially high demand.